In my next life, can i meet him again?

We cannot predict the next birth. Coarsely, next birth is based on aspects like: kamma, chuthi chiththa, habits, behaviors, and preferences. However, when you refer the Jathaka stories you can see a pattern. We can be born among those who near and dear to us (sometimes we can be re-born among our enemies as well). This could be because we have unfinished karma with those people.

However the situation, as a Buddhist; one cannot advice another to take a path towards re-incarnation. This is because we have little to no control of how, what or where we will be re-incarnated. And there are many things that can go wrong and one could end up spending eons in miserable and painful places. There is a story in Buddhist literature (Sorry I cannot recall the reference) that a man who had lust for a woman being re-born as a worm in her piles of excrement for thousands of lifetimes. My advice to you, learn Buddhism and attain Nirvana, the supreme bliss of them all.

1. From your explanation, you have been carrying this burden for more than 30 years. During this time you must have been angry and envying at his current wife. These are strong feelings that could become detriments to your path in sansara. And they could lead to many dark places in many a lifetimes in the expanse of endless time. IMHO, best option is wish them the best and move on. Be careful not to be angry or envious. Kind, and loving thoughts are the best.

2. There is no guarantee that your current parents will be your parents in next life. But you won't remember even if they did. So, best not to worry about such things. However, you can treat your parents well, take care of them to the best of your ability. Karma will follow you like a shadow.

3. If you are not enthusiastic about something in this life, chances are you could be the same in the next as well. If you didn't like to study, try to get to the bottom of its, as to 'Why don't I like like to study?'. It could be various reasons, like wrong approach, not the best subjects, or even uninteresting teachers. Alleviate these obstacles and continue your studies. It doesn't matter what your age is. The best time to change your trajectory of sansara is NOW. What you practice and form as habits in this life will be your foundation in the next. So, practicing studying and achieving success should not be put aside till the next birth.

It will be quite beneficial to you if you can learn the meaning and even chant karaniya metta sutta (a.k.a. metta sutta). Metta.

Question: At our death can we be reborn, find again the people who are dear to us, who have died and are in another life?

Thanissaro Bhikkhu: Yes, we can. As I explained yesterday, it’s through our kamma that we are related. The people to whom we are dear, or are dear to us: We have lots of kamma with them, so we’re likely to meet them again.

~ "The Karma of Mindfulness: The Buddha's Teachings on Sati & Kamma" https://www.dhammatalks.org/books/KarmaOfMindfulness/Section0016.html

Can i be finally united with him in my next life? Will my parent be the same in my next life?

For people to meet again in future lives there must be conditions favorable to that coming again together. Things conducive to it are having same beliefs, same generosity, same wisdom, same virtue, similar faculties & behavior, apples don't fall far from the tree in general.

To give an example if two people behaved like dogs and cultivated that behavior successfully, they would be born in the company of dogs and probably together still because their minds incline to it and conditions are favorable.

Coming back together may occur in circumstances where conditions such as gender are changed and one may become a dog, a horse or whatnot.

I love to be a doctor be part of medecins sans frontiers and cure people for free but in this life didn't succeed as my iq was not perfect in many fields in study.

Maybe you can and maybe you can't. This again depends on how you cultivate your mind. As an example if a dog looks up to humans and imitates their good behaviors, then even the dog can attain the human state, how much more a human who imitates the behaviors of wise people.

can't stop thinking of him every single day of my life.

When we think about something it is recognized and explored as a basis for pleasure, pain or equanimity.

Thoughts associated with pleasure are pleasant and inflame the mind, nothing is as obsessive as thoughts of infatuation with the sexuality.

Whatever you give frequent attention will become the inclination of the mind as the mind adapts to work efficiently. The pathways by which thoughts travel become developed & strengthened due to frequent use.

One can think of this as sending an electric current through wires, the charge will simply follow the path of least resistance and activate those structures.

If you give attention only to a positive aspect of an idea then that perception of beauty will be given a lot of attention and it will become the dominant perspective on it, the perception of beauty will become established and the perception of drawbacks will be given little to no weight & entertainment. This person will become "intoxicated" with beauty, due to not paying mind to the unattractiveness, then will behave irrationally seeing beauty in what is essentially not worthy of such regard & pursuit.

This site has many questions about the removal of distracting thoughts and development of good mental behavior.

Yes! You may be reborn in such a way that you can stay together with your life partner in future lives, if you both are in tune in conviction, virtue, generosity and discernment (wisdom).

And Nakula's mother said to the Blessed One: "Lord, ever since I as a young girl was brought to Nakula's father [to be his wife] when he was just a young boy, I am not conscious of being unfaithful to him even in mind, much less in body. We want to see one another not only in the present life but also in the life to come."

[The Blessed One said:] "If both husband & wife want to see one another not only in the present life but also in the life to come, they should be in tune [with each other] in conviction, in tune in virtue, in tune in generosity, and in tune in discernment. Then they will see one another not only in the present life but also in the life to come."
AN 4.55